1. Field of the Invention
The present invention relates to a ribbon cassette used in a recording apparatus, such as a thermal transfer printer, and a pancake accommodated in such a ribbon cassette. More particularly, the present invention relates to a ribbon cassette which allows precise recording as a result of stably running an ink ribbon while reducing rattling and rocking of cores, and a pancake accommodated in such a ribbon cassette.
2. Description of the Related Art
In conventional thermal transfer printers, recording operations are performed by transferring ink from an ink ribbon onto a recording sheet as a result of heating a thermal head. The ends of the ink ribbon are mounted to a take-up core and a supply core of a rotatably supported ribbon cassette. The ink ribbon, itself, is wound upon the take-up core and the supply core of the ribbon cassette. Rotation of the cores causes the ink ribbon to be conveyed to a recording sheet, and heating of the thermal head, disposed at the carriage, causes a desired recording operation to be performed on the recording sheet.
FIG. 5 illustrates such a ribbon cassette 4 which is placed at a top surface 2 of a carriage 1. A recording operation is performed, while the ink ribbon 3 in the ribbon cassette 4 is being wound up by driving the carriage 1. The ribbon cassette 4 includes a pair of cores 6A and 6B, a pair of pinch rollers 7A and 7B, and a plurality of guide 3 rollers 8. The pair of cores 6A and 6B are rotatably supported at a top case portion (not shown) and a bottom case portion 5A of a planar and substantially rectangular cassette case 5. The pair of pinch rollers 7A and 7B are rotatably supported for peeling the ink ribbon 3. The plurality of rollers 8 are provided for preserving the path of winding of the ink ribbon 3.
The pair of cores 6A and 6B are substantially cylindrical in shape. The ink ribbon 3, being either a thermally sublimating or a thermally melting type ink ribbon, is wound from both ends thereof upon the outer peripheral surface of each of the cores 6A and 6B, whereby a pancake is formed. When the ribbon cassette 4 is carried by the carriage 1 of the printer being used, the core 6A engages a take-up bobbin 9, serving as take-up mechanism shown in FIG. 6, and winds up the portion of the ink ribbon 3 that has been subjected to a recording operation. On the other hand, the core 6B engages a supply bobbin (having the same form as the take-up bobbin 9) disposed at the carriage 1, and supplies the ink ribbon 3 for performing a recording operation onto a recording sheet.
Bobbin fitting holes 10A and 10B are formed in the inner peripheral surfaces of the cores 6A and 6B, respectively. They are formed for fitting therein the take-up bobbin 9 and the supply bobbin (having the same shape as the take-up bobbin 9), respectively. A plurality of engaging protrusions 11, which are spaced in a peripheral direction, are formed at the bobbin fitting holes 10A and 10B. When the ribbon cassette 4 is being carried by the carriage 1, the engaging protrusions 11 mesh with a plurality of engaging protrusions 12 that are spaced in a peripheral direction along the outer peripheral surfaces of the take-up bobbin 9 and the supply bobbin.
The take-up core 6A, through the portions where the engaging protrusions 11 and 12 mesh, obtains rotational driving power from the take-up bobbin 9, serving as take-up mechanism. After an unused portion of the ink ribbon 3, wound upon the supply core 6B, has been subjected to a recording operation by the heat generated by a thermal head (not shown), the portion of the ink ribbon 3, which has been subjected to the recording operation, is wound upon the outer peripheral surface of the take-up core 6A. When the carriage 1 moves forward while the thermal head is in press-contact with the platen through the ink ribbon 3 and the recording sheet that are disposed between the thermal head and the platen, the supply core 6B is driven by the tension produced in the ink ribbon 3 that is wound upon the outer periphery of the supply core 6B. While the supply core 6B is being driven, the ink ribbon 3 is supplied to the recording sheet.
However, the above-described conventional cassette 4 has the following problem. The take-up bobbin 9 and the supply bobbin (having the same form as the take-up bobbin 9) that are fitted, respectively, to the cores 6A and 6B of the ribbon cassette 4 rotate by rotationally driving take-up shafts 9A of FIG. 6. During rotation, the take-up bobbin 9 and the supply bobbin are supported by supporting shafts 13 that are fixed to a base portion (not shown) of the carriage. The supporting shafts 13, however, are thin, being only about 1.6 mm thick. Therefore, when, during winding of the ink ribbon 3, the supporting shafts 13, which cannot withstand the tension in the ink ribbon, tilt, the rotational centers of the cores 6A and 6B, which engage the take-up bobbin 9 and the supply bobbin, respectively, move, causing the cores 6A and 6B to rock. Consequently, the ink ribbon 3 cannot be stably wound, thereby preventing precise recording operations.
Between the supporting shafts 13 and the take-up shafts 9A are provided gaps for making them rotatable. Between the take-up shafts 9A and the cores 6A and 6B are provided gaps for allowing insertion of the take-up shafts 9A into the cores 6A and 6B and allowing engagement of the take-up shafts 9A and the cores 6A and 6B. This results in great rattling of the cores 6A and 6B, causing the ink ribbon 3 to run unstably during recording operations.
In order to increase recording quality, the ink ribbon 3 must be run stably and the winding load must be kept constant. It has been found out that these can be achieved by reducing tilting and rattling of the cores 6A and 6B.